1. Field of the Invention
The present invention relates to a method for producing polyester, particularly biodegradable polyester.
2. Description of Related Art
In view of the environmental problems caused by non-degradable plastics discarded in farms, landfills, rivers and oceans, the plastics industry is devoted to the research and development of environment-friendly products which can be degraded by natural life. Microbial polyester is suitable not only to be made into environment-friendly products but also biodegradable plastic bottles, wrapping films, or water-proof films for fibers, papers or cards (serving as substitutes of non-degradable polyethylene or aluminum films), while it can also be utilized in the fields of biomedicine such as the manufacture of bone plates, bone nails, drug delivery or cell proliferation vehicles so as to achieve the purpose of degradation by life in a natural environment.
Though it was discovered in 1920s that microbes are capable of fermenting and generating microbial polyester using natural carbon sources, the production cost has been high due to a technical bottleneck in mass production, consequently preventing it from further uses. A number of techniques have been made in attempts to produce microbial polyester in large amounts, including transforming carbon source materials by natural bacteria strains so as to proceed with fermenting and producing microbial polyester. However, because of the common problems of contamination by undesirable strains during the culture of natural strains, complicated controlling strategies like limiting nitrogen sources, phosphorous sources or dissolved oxygen must be taken for high concentration of microbial polyester to be obtained. Thus, continuous fermentation cannot be employed, and the efficiency of mass production is limited. Besides, transgenic strains are also employed to transform carbon sources into microbial polyester, mainly by taking advantages of the rapid proliferation of microbes, such as E. coli, to proceed with mass production. However, transgenic strains must undergo a certain induction process upon expression of exogenous genes, and materials influencing gene expression must be removed from the media, making the costs of fermentation even higher, continuous fermentation impossible, and the efficiency poor in industrial scale uses.
Furthermore, the concentration of the microbial polyester is very low, which is produced by strains capable of utilizing phenol compounds that are not usable to other general microbes, or by salt-resistant strains that transform glucose or dissolvable starch. Thus, the process must be improved before it can be applied to industry-scale mass production.